Abstract: BI2.00006 : Ion Acoustic Waves in Ultracold Neutral Plasmas

Author:

Thomas Killian
(Rice University)

Ultracold neutral plasmas, which are created by photoionizing
laser cooled
atoms near the ionization threshold, have been extensively
studied in order
to probe strong Coulomb coupling effects, low-energy atomic
processes,
equilibration, and collective phenomena [1]. The experimental
study of
collective modes, however, has previously been limited to phenomena
involving electrons. By spatially modulating the intensity
pattern of the
photoionizing laser, we are now able to create controlled density
perturbations on the plasma, which enables study of ion
collective behavior.
Periodic modulation excites ion acoustic waves [2]. We have also
created two
distinct plasmas that stream into each other. In the hydrodynamic
regime,
the central gap between the two plasmas splits into two density
``holes''
that propagate away from the plasma center at the ion acoustic
velocity. At
lower densities and higher particle velocities, plasmas are less
collisional, and we observe kinetic effects such as plasma streams
penetrating each other, with a penetration depth that reflects
the ion
stopping power.
This general technique for sculpting the density opens many new
possibilities, such as investigation of non-linear phenomena,
instabilities,
and shock waves in the ultracold regime, and determination of the
effects of
strong coupling on dispersion relations. The low temperature,
small size,
plasma expansion, and strongly coupled nature of ultracold
plasmas make
these studies fundamentally interesting. They may also shed light
on similar
phenomena in high energy density, laser-produced plasmas that can
be near
the strongly coupled regime.
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[1] T. C. Killian, T. Pattard, Thomas Pohl, and J. M. Rost, Phys.
Rep., 449, 77 (2007).
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[2] J. Castro, P. McQuillen, and T. C. Killian, Phys. Rev. Lett.
105, 065004 (2010).

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.DPP.BI2.6